linux-kernel - Re: [PATCH] 9p/virtio: restrict page pinning to user_backed

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Message-ID: <aUMlUDBnBs8Bdqg0@codewreck.org>
Date: Thu, 18 Dec 2025 06:49:04 +0900
From: asmadeus@...ewreck.org
To: Christian Schoenebeck <linux_oss@...debyte.com>
Cc: Eric Van Hensbergen <ericvh@...nel.org>,
	Latchesar Ionkov <lucho@...kov.net>,
	Chris Arges <carges@...udflare.com>, v9fs@...ts.linux.dev,
	linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
	Matthew Wilcox <willy@...radead.org>, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] 9p/virtio: restrict page pinning to user_backed_iter()
 iovec

Christian Schoenebeck wrote on Wed, Dec 17, 2025 at 02:41:31PM +0100:
> Something's seriously messed up with 9p cache right now. With today's git 
> master I do get data corruption in any 9p cache mode, including cache=mmap, 
> only cache=none behaves clean.

Ugh...

> With this patch applied though it gets even worse as I can't even boot due to 
> immediate 9p data corruption. Could be coincidence, as I get corruption 
> without this patch in any cache mode as well, but at least I have to try much 
> harder to trigger it.

As said before don't bother with this patch, it's definitely wrong --
we can't just use data->kvec->iov_base for bvec or folioq iters, so
there *will* be corruptions with this patch.

I'll try to see if I can produce anything wrong with master...
-- 
Dominique